ALL it takes is one good new project to turn a swath of cityscape around.

Ever since Axel Stawski‘s glass-wrapped office building went up at 505 Fifth Ave., the blocks adjoining the once-miserable northeast corner of Fifth and 42nd Street have taken off.

The corner, long home to a tacky flea market and an empty lot, blighted the area for decades. The Stawski project overlooking Bryant Park is not the only reason for new activity nearby, but it certainly doesn’t hurt.

The most visible evidence of change for the better is the arrival of the new Taipei Economic and Cultural Office next door at 1 E. 42nd St., where the long-empty and formerly filthy 11-story building has been spiffily cleaned up.

And the investment sale market nearby is going wild, with a quartet of solid addresses on the avenue’s east side between 42nd and 45th streets about to change hands.

The so-called Zeus portfolio totals more than 595,000 square feet of office and retail space, with the lion’s share of office space – 319,000 feet – at 535 Fifth.

Nos. 535 and 545 comprise a rare full blockfront on the avenue. The buildings are 90 percent leased following $42 million in capital improvements over the past nine years.

The deal was brokered by Cushman & Wakefield’s Richard Baxter, who declined comment.

Meanwhile, publicly traded SL Green appears on the brink of buying 521 Fifth, the 1929-vintage tower between 43rd and 44th streets, from RFR Holdings. Sources said a sale contract has been signed for an unspecified amount.

If the deal goes through, it would be a blast from the past for SL Green, which in recent years has been increasingly focused on modern, Class-A properties rather than the older Class-B ones in which company founder Stephen L. Green specialized.

Seattle-based Callison Architecture’s New York office has its work cut out: It’s been tapped by the Port Authority to work on the shopping arcade inside the Santiago Calatrava-designed PATH terminal now under way at Ground Zero, and also on the retail space the PA wants to build at the bases of Larry Silverstein‘s planned office towers 3 and 4.

Not surprisingly, Callison needed more elbow room, so it’s quadrupling its New York space. The firm is moving from 2,500 square feet at 80 W. 40th St. to 10,000 feet – the whole 10th floor – at 100 Fifth Ave.

Israel-based bath and cosmetics chain Sabon is bringing the Dead Sea to Sixth Avenue. Sabon just signed a lease for the last available storefront on the west side of the avenue between 55th and 56th streets.

The 800-square-foot deal at 101 W. 55th was for $275 per square foot, according to ZE Realty Group’s Scott Edlitz, who repped the landlord along with Josh Roth. The tenant was repped by IGDNYC Inc.

Sabon says its products are “handmade from the Israeli countryside and the Dead Sea.”

Although the square footage is small, the new lease typifies the upscaling of Sixth Avenue near Central Park South; other new tenants at 101 W. 55th include accessory chain Laila Rowe and Washington Mutual bank.

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Law firm Entwistle & Cappucci, which specializes in corporate, transactional and securities litigation, is nearly doubling its Manhattan office space. The firm is moving from 299 Park Ave. to 280 Park Ave., via a nine-year, 20,000-square-foot sublease from Bank of America.

Cushman & Wakefield’s Owen Hane and John Cefaly represented Entwistle & Cappucci in negotiating both the new sublease and in terminating its old one at 299 Park.

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One of Times Square’s biggest and most visible supersign spaces is up for grabs. Prudential Financial’s multicolor display at 3 Times Square, the Reuters headquarters at Seventh Avenue and 42nd Street, will come down early next year.

The wraparound, 6,000-square-foot space over the bustling corner will be available as of April 1, says Rudin organization leasing chief John Gilbert. The Prudential display is right on top of J.P. Morgan Chase’s sign, which is staying put.

Prudential Financial’s departure will mark the final chapter in the company’s Times Square presence. It once owned the four development sites at the “Crossroads of the World.” When it sold the site of 3 Times Square to the Rudin organization in 1998, it kept leasing rights to the sign space.